Python Programming – Deleting List Elements

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Python Programming – Deleting List Elements

Deleting list elements

To remove a list element, one can use either the del statement (if you know the element index to delete) or remove () method (if you do not know the element index, but the element itself, discussed in section 4.1.9). The following example depicts the deletion of an element using the del statement.

>>> a= [ ' spam ' , ' eggs ' , 100 , 1234 ]
>>> del a [ 1 ]
>>> a
[ ' spam ' , 100 , 1234 ]

The del statement can also be used to explicitly remove the entire list.

>>> a= [ ' spam ' , ' eggs ' , 100 , 1234 ]
>>> del a 
>>> a
Traceback ( most recent call last ) :
File " <stdin> " , line 1 , in <module>
NameError: name ' a ' is not defined

The following is an interesting case of the del statement:

>>> a= [ ' spam ' , ' eggs ' , 100 , 1234 ]
>>> del a [ 1 ] , a [ 1 ]
>>> a
[ ' spam ' , 1234 ]

It should be noted that the same index is deleted twice. As soon as an element is deleted, the indices of succeeding elements are changed. So deleting an index element n times, would actually delete n elements.

It is also possible to delete multiple items from a list.

>>> a= [ ' spam ' , ' eggs ' , 100 , 1234 ]
>>> a [ 1 : 3 ] = [ ]
>>> a
[ ' spam ' , 1234 ]

Swapping lists

There might be a scenario in which multiple lists need to be swapped among themselves. This is can done easily using multiple assignments expression.

>>> a= [ 10 , 20 , 30 ] 
>>> b= [ 40 , 50 , 60 ] 
>>> c= [ 70 , 80 , 90 ]
>>> a , b , c=c , a , b 
>>> a
[ 70 , 80 , 90 ] 
>>> b
[ 10 , 20 , 30 ]
>>> c
[ 40 , 50 , 60 ]

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